Manufacturing of silicon chips or wafers typically involves a myriad of processing steps, such as photolithography. In photolithography, a wafer surface deposited with a photoresist is exposed to a radiation source through a patterned reticle. The radiation source, such as ultraviolet light, travels along a radiation route and is incident on or reflected off a pattern reticle in order to project the patterns of the reticle onto the wafer. The wafer is then subjected to development and etching processes for removing undesired portions while leaving the reticle-defined patterns thereon.
As the industry continues the trend of decreasing device size, the line width on wafers are scaled down and the device count is increased accordingly. On one hand, the fidelity requirement of the reticle pattern is getting more stringent. On the other hand, error-free transformation of the reticle pattern image onto the wafer also plays an important role in determining the quality of the final semiconductor product. As a result, a cleared environment around the pattered reticle is necessary. In addition, it is important to keep the operative surface of the reticle away from foreign particles or contaminants that could otherwise obstruct the traveling path of the radiation or roughen the reticle surface such that the no defects would occur, such as undesired open or closed circuits. Thus, an effective shielding mechanism for the reticle is needed.